The present invention relates to an RF (Radio Frequency) transmission circuit, a complex digital synthesizer, and an MRI (Magnetic Resonance Imaging) apparatus, and particularly to an RF transmission circuit, a complex digital synthesizer, and an MRI apparatus which are based on the circuit digitization so that the stability of signal quantity can be enhanced and the cost can be reduced.
FIG. 15 is a block diagram showing a prior art RF transmission circuit which can be used with a MRI apparatus.
This RF transmission circuit 10J includes a digital circuit section and an analog circuit section.
The digital circuit section includes a system interface 20J which receives control data from a high-ranking circuit which controls the scanning, a digital synthesizer 30J which generates a reference carrier frequency signal data under control of the system interface 20J, and an RF envelope register 71 which holds RF envelope data released by the system interface 20J.
The analog circuit section includes a D/A converter 51 which converts the reference carrier frequency signal data into an analog reference carrier frequency signal a0, a band-pass filter 52 which eliminates the alias harmonics emerging in the analog reference carrier frequency signal a0 and releases a resulting reference carrier frequency signal a1, an oscillation circuit 53 and frequency demultiplying circuit 54 which produce a mixing signal for up-converting the carrier frequency to a resonant frequency necessary at an intended static magnetic field strength, a band-pass filter 55 which eliminates spurious frequency components from the mixing signal to produce a mixing signal a2, a carrier mixer 56 which combines the reference carrier frequency signal a1 and the mixing signal a2 and releases a resulting carrier frequency signal a3, a band-pass filter 57 which eliminates spurious frequency components from the carrier frequency signal a3 to produce a carrier frequency signal a4, a D/A converter 72 which converts the RF envelope data into an analog RF envelope signal e1, a band-pass filter 73 which eliminates the alias harmonics emerging in the analog RF envelope signal e1 and releases a resulting RF envelope signal e2, an RF envelope mixer 58 which combines the carrier frequency signal a4 and the RF envelope signal e2 and releases a resulting analog RF pulse signal a5, a band-pass filter 81J which eliminates spurious frequency components from the analog RF pulse signal a5 and releases a resulting RF pulse signal, a programmable-gain amplifier 82J, and a send/receive selector switch 83J.
The above-mentioned conventional RF transmission circuit 10J has much of its process, particularly the mixing process and associated band-pass filtering process, done by the analog circuit section.
However, analog component parts inevitably have the disparity of characteristics, which results problematically in the instability of signal quantity. The need of choosing analog component parts having less disparity of characteristics results problematically in an increased cost.